Typically, the current sensors concerned operate for currents of 10 μA to 5000 A, especially for high currents of over 100 A.
The term “non-magnetic material” here below designates a material that does not show magnetization that is measurable in a zero field. Such a non-magnetic material is therefore devoid of iron, cobalt and nickel.
A prior-art current sensor comprises:                an electrical conductor extending along a direction X, and        a known magnetic field sensor fixed without any degree of freedom to this electrical conductor.        
The known magnetic field sensor comprises at least one magnetoresistive rod comprising a stack of at least:                a first magnetic layer, called a “pinned layer” the magnetization direction of which is fixed and perpendicular to the longitudinal direction to within plus or minus 10°,        a second magnetic layer, called a “free layer”, the axis of easiest magnetization of which is parallel to the longitudinal direction and the magnetization of which can turn when it is subjected to a magnetic field to be measured, and        a non-magnetic layer, called a “spacer” interposed between the two above layers to form a tunnel junction or a spin valve.        the length of the rod, in its longitudinal direction, being at least ten times greater than its greatest width in a transverse direction perpendicular to the longitudinal direction and parallel to the layers of the stack.        
In the known sensors, the length of the bar in the longitudinal direction is at least ten times greater than its greater length in the crosswise direction perpendicular to the longitudinal direction and parallel to the layers of the stack.
Such a known current sensor is described for example in the patent application US2004/0137275. Another known sensor is described in the following document A0:
Bill Drafts, “Magnetoresistive Current Sensor Improves Motor Drive Performance”, Pacific Scientific—OECO, 4607 SE International Way, Milwaukie, Oreg. 97222.
In these sensors, the shape ratio or aspect ratio of the magnetic rods is great, i.e. greater than 20, 40 or 100. The term “shape ratio” or “aspect ratio” designates the ratio of the length of the magnetoresistive rod to its width.
This high shape ratio is necessary to be able to adjust the sensitivity of the magnetoresistive rod over a very wide range and therefore to enable this magnetoresistive rod to measure magnetic fields of high intensity. Indeed, the greater the shape ratio, the more difficult it is to cause the direction of magnetization of the free layer to turn. Magnetoresistive rods with a shape ratio of over 1000 have therefore been proposed. However, these magnetoresistive rods are then very long, making the sensor bulky.
Furthermore, magnetoresistive rods show hysteresis. Indeed, the variation of their resistance as a function of a magnetic field to be measured is not the same depending on whether the magnetic field to be measured increases or diminishes. The solution presently applied to resolve this problem uses auxiliary sources that generate a magnetic field in parallel to the direction of easiest magnetization of the free layer. Typically, these magnetic field auxiliary sources are permanent magnets or electrical conductors. The presence of these auxiliary sources increases the complexity of the sensor and its space requirement.
Prior art is known from: U.S. Pat. No. 6,117,569A, US2008/272771 A1 and DE 100 54 016 A1.